Ion pump



PYI;A 6i 1965* P; A.r REDHEAD 31,176,906?

rom BUMP Aug.. 2.15,. 1962 2 Sheds-Sheet l PAUL A. REDHEAD PATENT AGENTUnited States Patent O M' 3,1%,9-35 IGN PUMP Paul A. Redhead, ttawa,@nto io, anada, assigner to National Research Council, @travi/a,Gntario, Canada, a body corporate ci Canada Filed Aug. 23, w62, Ser. NZtl i3 Claims. (Qi. 23u-ne?) This invention relates to a cold cathodeionization vacuum pump and more particularly to a magnetron typeionization vacuum pump having a discharge region in which electric andmagnetic lields are produced substantially at right angles Theproduction of low pressures has been achieved in the past by the use ofa combination of mechanical pumps and diiusion pumps. In recent yearsvarious types of ionization pumps have been developed. These pumps diierfrom the mechanical and diffusion pumps in that they do not remove gasfrom the vacuum system but rather by immobilizing the gas within thesystem by a combination of chemical adsorption and entrapping of theions of gas. ionization pumps contain no lluid and Vtherefore have onesalient advantage over diffusion pumps which use a uid e.g. oil ormercury which can reach the vacuum system causing contamination.

There are two general types of ionization pumps known and in use at thepresent time. In the first type, which is known as a sputter-ion pump,the positive ions formed in the discharge region bombard a metalsurface, usually titanium and sputter metal atoms from this surface. Thesputtered material condenses on other portions of the device providedfor this purpose, entrapping and adsorbing the chemically active (otherthan inert) gases in the system. The second type of pump, which is knownas a getter-ion pump contains a source of metal usually titanium, whichis evaporated. This evaporated material condenses on surfaces providedin the system, entrapping and absorbing the chemically active gases.

The sputter-ion type of pump is in more widespread use in that it doesnot require a source of heater current for an evaporator which is thecase with the getter-ion type.

All ionization pumps using a magnet-ic lield in use at the present timeare of the parallel-ield type in that the electric and magnetic fieldsare parallel. Because of the geometry of parallel-held pump the magnetsrequired to produce the magnetic iield are large and heavy.

It is an object ot the present invention `to provide an ionizationvacuum pump which is light in weight, simple in design, and has greatlyincreased pumping speeds in relation to its size and weight.

It is another object of the invention to provide an ionization pump thathas its pumping area separated from the discharge region allowing wideflexibility in the design of the pumping region.

Another object oi this invention is to provide an ionization pump inwhich the magnetic field structure forms part of or is in closeproximity to the envelope thus achieving a lighter and more ellicientdevice.

Another object of this invention is to provide a pump Whose geometry issuch that a tube of large diameter can be readily used to connect thepump to the system required to be evacuated, allowing high pumpingspeed.

These and other obiects of the invention are realized by providing anionization pump comprising a gas-tight enclosure delining twointerconnected volumes, the iirst said volume deuing a discharge regionand the second said volume defining a pumping region, means forconnecting the pumping region to a system that is to be evacusted,` ametallic structure mounted in the pumping "region to provide metallicatoms for the absorbing Patented Apr. d, 1%55 ICC of the gas moleculesbeing pumped, a magnetic circuit `forming part of said enclosure andhaving poles forming a magnet gap region therebetween, said magnet gapregion being said discharge region, a permanent magnet in said magneticcircuit to produce a strong magnetic lield in the discharge region, acathode positioned adjacent the interconnection between the pumpingregion and the discharge region, an anode positioned adjacent the magnetgap and opposite the said cathode, and lead means to supply a potentialto the anode to produce an electric field in the discharge regio-n, saidelectric lield being transverse to the said magnetic field.

In drawings which illustrate embodiments of the inventon,

FIGURE l is a cross-sectional view of a sputterion according to theinvention, v

FGURE 2 shows section A-A of FGURE 1,

FIGURE 3 is a three-quarter View of a sputter-ion pump according to theinvention showing the positioning of the permanent magnets,

FGURE 4 is a plural version of the pump capable of increased pump-ingspeeds.

Referring to the drawings, FIGURE l shows a sputter-ion pump accordingto the invention having an envelope indicated generally as l, formed byan upper pole piece '7 and a lower pole piece S, a generally cylindricalshaped outer barrier wall i3 made of stainless steel or othernon-magnetic material, a glass-to-metal seal d and tubular member ilwhich would be connected to the system to be evacuated. This envelopedenes a first Volume shown generally as 2, to be referred to below asthe pumping region. Pole pieces 7 and 8 have raised portions extendingtowards each other, forming north and south magnetic poles N and S anddening a second region (magnet gap) between them shown generally as 3.The poles should be relatively close to each other so that a strongmagnetic ield can be produced in the magnet gap. This requirementhowever must be consistent with the need to provide space for adischarge of sumcient size to be formed in the gap. The faces of themagnetic poles are covered with thin sheets llt) oi a metal preferablytitanium. Permanent magnets ld which are magnetized along their lengthare positioned to contact pole piece and 8 which are preferably made oflow reluctance mild steel to form a magnetic circuit md provide a strongmagnetic field in magnet gap 3. Cylindrical tubes 9 of sheet titaniumare positioned adjacent the interconnection between pumping region 2 andmagnet gap 3 and form, with sheets itl, a

cathode. An anode in the form of a cylindrical ring 121 is positionedoutwardly of magnet gap 3. The cathode 9 and itl and pole pieces 7 and Sare operated at ground potential and anode l2 is operated at highpositive potential with the result that an electric iield is set up inthe magnet gap region 3 generally at right-angles to the magnetic iieldmentioned above. A sputter cathode d mounted on rod 5 extending throughglass seal 6 is positioned centrally of pumping region 2 and generallyfacing slit if formed by tubes 9. Sputter cathode d is formed of acylindrical sheet or solid rod of titanium. Anode i2 is held in positionby rod l5 which passes through barrier wall i3 by means ofglass-to-metal or ceramic-metal seal ld. Rod l5 also acts as anelectrical lead for the anode and would be connected at 17 to a sourceoffhigh direct current voltage. Barrier Wall 13 is sealed to upper polepieces 7 by means of an insert ring 32 which is welded or brazed tobarrier wall i3 and bolted to pole iece '7 by several bolts 3l. A goldwireY O-ring seal 33 is compressed by the tightening of bolts 31providing the required seal between pole piece 7 and insert ring 32.Barrier wall i3 is welded or brazed to lower pole piece d. Cylindricalmember il. is connected by means Ythe pumping region.

- region.

of a glass-to-metal seal to the, tubulation 19 of the external system.The glass-to-metal seals can be standard Kovar-glass seals orceramic-metal seals.

FIGURE 2 is acrosssectional view^AA through the pump shown in FIGURE 1and shows a method of mounting the permanent magnets 14. Although twelvemagnets are shown in this figure the number could be varied yquitewidely. If pole pieces 7 and 8 shown in FIGURE 1 were constructed ofpermanent magnet material a moreV efiicient device would be realizedwith the result that smaller or fewer permanent magnets would beait/esce required.v From this figure it will be seen that the device yas Ashown in FIG. l is, with the exception of the magnets, a figure ofrotation and that the discharge region (magnet gap region) is an annuluscompletely encircling The discharge region which acts as a source ofpositive ions is able to supply ions to converge on the sputter cathodefrom a 360 sector. It can be seen that this results in a very efficientdevice.

In operationa discharge is established in the region bounded by the polefaces, the anode and the cathode. This discharge region coincidesgenerally with the magnet gap region 3 mentioned above. Stray electronsin Athe discharge region are attracted towards the anode cules and ifthe electrons have sufficient energy they will ionize the gas moleculesand produce electrons and pos-itive ions. These positive ions areattracted towards the cathode and a large proportion will havesufiicient energy to pass through slit 16 in the cathode tubes into thepumping region. These positive ions strike the sputter cathode 4 wheresome will be trapped in the sputter cathode and others upon collisionwith the sputter cathode will disintegrate portions of the cathode. Thedisintegrated materialV from the cathode is sputtered over the interiorof the cathode tubes where it condenses entrapping and absorbing furthergas molecules. This 'gives rise to pumping action. the discharge regionoverlap to some extent with the -discharge extending some distance intothe pumping region and pumping action taking place in the discharge Itshould be pointed out that the action described here as absorption alsoincludes the phenomenon usually described as adsorption.

The crossed electric and magnetic fields produce a discharge regionsimilar to that in a magnetron. Electrons on their Way toward the anodetravel in spiral orbits which increases greatly the probability of theirstriking and ionizing a gas molecule. This results in highly increasedefficiency. Typical values for the anode voltage Would be, for example,2 to 7 kv. and for the magnetic flux density in the gap, 1000 gausses. vIt should be realized however that these values could be varied quitewidely and still obtain good pumping performance.

FIGURE 3 is a three-quarter View of a Version of the pump showingexternal features especially the method of positioning of magnets 14.

If very fast pumping speeds are required, a plural version of the pumpcould be built and FIGURE 4 shows an example Vof a sputter-ion pumpthatrwould have parallel pumping action at three positions.

In the above description a typical example of a method of producingthese pumps has been shown. It should be realized that theinvention-claimed in this application is directed to the novelarrangements of the magnetic circuit, the pumping region, the dischargeregion and the different electrodes positioned therein.V The method ofmanufacture of these pumps could vary considerably within the scope ofthe invention. For example, the upper andlower pole pieces and thepermanent magnets Vcould be made as a unitary structure out of magneticmaterial. The stainless steel barrier Vwall could be in the form of athinsheet in contact with a portion of the The pumping region and innersurface of this unitary structure. The anode structure positioning rodcould bey taken through both the stainless steel sheet and the magneticmaterial by means of a glass-to-metal seal. In some cases, the barrierwall might be eliminated altogether. In ionization pumps, titanium hasbeen the metal most generally used to absorb and entrap the gasmolecules. Other suitable metals such as molybdenum, tantalum, tungsten,zirconium, iron, y calcium, barium, etc., might Vbe used. The presentinvention is not primarily concerned with the metal used.

What is claimed is:

1. An ion pump comprising a cathode and an anode spaced apart :to definetherebetween a glow-discharge zone in which gas ionization isaccomplished, electrical connections to said cathode and anode whichWhen connected to an external electrical potentialV source will cause anelectrical field to be established between the anode and cathode, amagnetic circuit arranged to establish a magnetic field Itransverse tothe said electrical field, the glowdischarge zone having a longdimension transverse to the magnetic field which is at least severaltimes greater than that dimension of the zone which is parallel to themagnetic field, a sorption zone in which ions and molecules are sorbed,the cathode extending along said long dimension, the cathode serving toseparate the glow-discharge and sorption zones, the cathode beingpositioned to permit ready escape of positive ions from theglow-discharge zone into the sorption zone, a source of sorption metalpositioned within said sorption zone,.said source being a sputtercathode positioned in said sorption zone Such that positive ions fromthe glow-discharge zone can strike its surface and disintegrate metaltherefrom, means defining a substantial sorption area inthe sorptionzone on which sorption metal is deposited, the sorption area beingoutside of the glow-discharge zone, and being substan-' tially greaterthan the area of cathode separating the glow-discharge zone from thesorption zone, `and means to connect said sorption zone to a structureto be evacuated.

2. An ion pump comprising an anode and perforated `cathode connected toa source of electrical potential so the glow-discharge zone can strikeits surface and disintegrate metal therefrom, a substantial sorptionarea within the sorption zone on which sorption metal vapors areVcondensed, the sorption area being outside of the glowdischarge zone,and means to connect said sorption zone to a structure to be evacuated.

3. A cold cathode ionization pump comprising in combination: meansdefining a glow-discharge region for ionizing gases therein, said meanscomprising anode means and cathode means, said anode and cathode meansbeing arranged to provide an electric field in said glow-dischargeregion; magnetic field producing means for providing a magnetic fieldItransverse |to said electric field; said glow-discharge defining meansbeing arranged to define a long characteristic dimension for said regionhaving atleast a major component transverse to said magnetic field andVa short characteristic dimension having at least aV major componentparallel to said magnetic field; means defining a sorption regionseparate from said glow-discharge region and connected to it such thations originating 'in said glow-discharge region can, enter directly intosaid Vsorption zone; a source of sorption metal positioned in saidsorption region capable of disintegration by ion bombardment by ionsentering said sorption region from said glow-discharge region; and meansto connect said sorption zone to a structure to be evacuated.

4. A cold cathode ionization pump as in claim 3 in which said cathodemeans is arranged to provide openings therein for gas conductance.

5. A cold cathode ionization pump as in claim 3 in which said cathodemeans comprises a plurality of spaced cathode plates defining a gasconductance space therebetween.

6. An ionization pump as in claim 2 in which said perforated cathode isdefined by at least two cathode plates defining an aperturetherebetween.

7. An ionization pump as in claim 2 in which said perforated cathode isdefined by a pair of cathode rings, said rings being coaxial andlongitudinally spaced to define a gas conductance path between saidionization and sorption zones.

8. An ionization pump as in claim 3 in which said anode means comprisesa plate and said cathode means comprises a second plate structure spacedfrom and parallel to said anode plate, said pump further comprisingsecondary cathodes consisting of members extending transversely fromsaid cathode means towards said anode means.

9. An ionization pump as in claim 3 in which the magnetic tieldproducing means comprises a permanent magnet structure, said structurebeing horseshoe shaped in cross-section and spanning the far side ofsaid anode means, such that said magnet struc-ture defines a partialenvelope housing lthe ionization region.

10. A cold cathode ionization pump of the sputter-ion type comprising agas tight enclosure defining two interconnected volumes, the first saidvolume being a discharge region and the second said volume being apumping region, means for connecting the pumping region to a system thatis to be evacuated, a sputter cathode mounted in the pumping region toprovide metallic atoms for the absorbing of the gas molecules beingpumped, a magnetic circuit forming part of said enclosure and havingpoles forming a magnet gap region therebetween, said magnet gap regionbeing said discharge region, a permanent magnet in said magnetic circuitto produce a magnetic field in the discharge region, a cathode having asurface capable of absorbing gas molecules positioned ad jacent theinterconnection between the pumping region and the discharge region, ananode positioned adjacent the magnet gap region and opposite the saidcathode, and lead means to supply a potential to the anode to produce anelectric field in the discharge region, said electric field beingtransverse to the said magnetic field.

11. A cold cathode ionization pump comprising in combination: meansdefining a glow-discharge region for ionizing gases therein, said meanscomprising an anode and a cathode arranged to provide an electricalfield in said glow-discharge electric lield; magnetic field producingmeans for providing a magnetic lield transverse to said electric field,said magnetic iield producing means comprising a permanent magnetstructure, horseshoe shaped in cross-section and partially encirclingsaid anode, arranged to provide a portion of the envelope defining saidglow-discharge region; said glow-discharge defining means being arrangedto define a long characteristic dimension for said region having atleast a maior component transverse to said magnetic field and a shortdimension having at least a major component parallel to said magnetictield; means defining a sorption region separate from saidglow-discharge region and connected to it such that ions originating insaid glowfdischarge region can enter directly into said sorption zone;and a sputter cathode mounted in the said sorption region to provide me-|tallic atoms for the sorbing of the gas molecules being pumped.

12. A cold cathode ionization pump as in claim ll in which the saidsorption region comprises tubulation in Ithe central :region surroundedby said ionization region, the inner surface of said tubulationproviding said sorption area and said tubulation connected to a systemto be pumped to provide a high. conductance gas inlet passage for saidpump.

13. An ionization pump as in claim 1 in which a plud rality of stackedglow-discharge zones are provided adjacent a common sorption zone.

No references cited.

LAURENCE V. EFNER, Primary Examiner.

WARREN E. COLEMAN, Examiner.

1. AN ION PUMP COMPRISING A CATHODE AND AN ANODE SPACED APART TO DEFINETHEREBETWEEN A GLOW-DISCHARGE ZONE IN WHICH GAS IONIZATON ISACCOMPLISHED, ELECTRICAL CONNECTIONS TO SAID CATHODE AND ANODE WHICHWHEN CONNECTED TO AN EXTERNAL ELECTRICAL POTENTIAL SOURCE WILL CAUSE ANELECTRICAL FIELD TO BE ESTABLISHED BETWEEN THE ANODE AND CATHODE, AMAGNETIC CIRCUIT ARRANGED TO ESTABLISH A MAGNETIC FIELD TRANSVERSE TOTHE SAID ELECTRICAL FIELD, THE GLOWDISCHARGE ZONE HAVING A LONGDIMENSION TRANSVERSE TO THE MAGNETIC FIELD WICH IS AT LEAST SEVERALTIMES GREATER THAN THAT DIMENSION OF THE ZONE WHICH IS PARALLEL TO THEMAGNETIC FILED, A SORPTION ZONE IN WIXH IONS AND MOLECULES ARE SORBED,THE CATHODE EXTENDING ALONG SAID LONG DIMENSION, THE CATHODE SERVING TOSEPARATE THE GLOW-DISCHARGE AND SORPTION ZONES, THE CATHODE BEINGPOSITIONED TO PERMIT READY ESCAPE OF POSITIVE IONS FROM THEGLOW-DISCHARGE ZONE INTO THE SORPTION ZONE, A SOURCE OF SORPTION METALPOSITIONED WITHIN SAID SORPTION ZONE, SAID SOURCE BEING A SPUTTERCATHODE POSITIONED IN SAID SORPTION ZONE SUCH THAT POSITIVE IONS FROMTHE GLOW-DISCHARGE ZONE CAN STRIKE ITS SURFACE AND DISINTEGRATE METALTHEREFROM MEANS DEFINING A SUBSTANTIAL SORPTION AREA IN THE SORPTIONZONE ON WHICH SORPTION METAL IS DEPOSITED, THE SORPTION AREA BEINGOUTSIDE OF THE GLOW-DISCHARGE ZONE, AND BEING SUBSTANTIALLY GREATER THANTHE AREA OF CATHODE SEPARATING THE GLOW-DISCHARGE ZONE FROM THE SORPTIONZONE, AND MEANS TO CONNECT SAID SORPTION ZONE TO A STURCTURE TO BEEVACUATED.